Hepatitis C virus (HCV) is a (+)-sense single-stranded RNA virus in the Flaviviridae family. Its 9.6 kb genome encodes for approximately 10 proteins, including the structural capsid and envelope proteins, as well as the nonstructural proteins NS3 (protease and helicase) and NS5B (polymerase). The viral RNA-dependent RNA polymerase (RdRp) is responsible both for generating the intermediate minus-strand RNA template and for the synthesis of progeny positive-strand genomic RNA (Ishii et al., Hepatology, 1227 (1999)). RdRp is used only in the replication of RNA viruses and has very strict template specificities. Thus, RNA-dependent RNA polymerase enzymes, including HCV RdRp, are ideal targets for antiviral drugs.
HCV has been implicated as the major causative agent in non-A, non-B hepatitis (NANBH), particularly in blood-associated NANBH (BB-NANBH) (see, International Patent Application Publication No. WO 89/04669 and European Patent Application Publication No. EP 381 216). NANBH is to be distinguished from other types of viral-induced liver disease, such as hepatitis A virus (HAV), hepatitis B virus (HBV), delta hepatitis virus (HDV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV), as well as from other forms of liver disease such as alcoholism and primary biliar cirrhosis.
HCV has been shown to be capable of establishing a persistent infection and has been implicated in cirrhosis of the liver and in induction of hepatocellular carcinoma. HCV is believed to have infected approximately 3% of the worldwide population. The prognosis for patients suffering from HCV infection is currently poor. HCV infection is more difficult to treat than other forms of hepatitis due to the lack of immunity or remission associated with HCV infection. Current data indicates a less than 50% survival rate at four years post cirrhosis diagnosis. Patients diagnosed with localized resectable hepatocellular carcinoma have a five-year survival rate of 10–30%, whereas those with localized unresectable hepatocellular carcinoma have a five-year survival rate of less than 1%.
Existing therapies for HCV are limited, and only a few inhibitors of HCV RNA-dependent RNA polymerase are known. There is thus a need to identify additional HCV RdRp inhibitors and to identify the structural features required for potent HCV RdRp inhibitory activity.